BOE waste liquid treatment method and device

Abstract

The invention discloses a BOE waste liquid treatment method and device. The method comprises the following steps: replacing hydrogen fluoride in BOE waste liquid with sulfuric acid, evaporating, fractionating and recovering hydrofluoric acid, neutralizing evaporated residual liquid with ammonia to obtain a fluorine-containing ammonium sulfate solution, defluorinating with fluorgypsum slurry to obtain a low-fluorine ammonium sulfate solution, and concentrating and crystallizing to obtain an ammonium sulfate product. The BOE waste liquid is treated by adopting the scheme, the bottleneck of the market capacity of ammonium bifluoride is avoided, the hydrofluoric acid product and the ammonium sulfate product with huge market capacity are produced, the value orientation of turning waste into wealth, circular economy and environmental protection is really realized, and the method is suitable for industrial popularization and application.

Description

Technical Field

[0001] The present invention relates to the technical field of waste liquid recycling, and in particular to a BOE waste liquid treatment method and device. Background Art

[0002] BOE (Buffered Oxide Etch), buffered oxide etching solution, referred to as "buffered etching solution". It is made by mixing hydrofluoric acid (HF) and ammonium fluoride (NH4F) in different proportions. It is used for etching semiconductor components (such as chips). HF mainly plays an etching reaction role, and NH4F is used as a buffer; HF reacts with silicon, and NH4F fixes H + The concentration of BOE etching solution is adjusted to maintain a certain etching rate. After the BOE etching solution is used for a certain period of time, it is discharged as waste liquid and becomes BOE waste liquid.

[0003] The main components of BOE waste liquid are ammonium fluoride (NH4F) and ammonium bifluoride (NH4HF2), and it also contains a small amount of ammonium fluorosilicate. It is hazardous waste, and most semiconductor factories entrust qualified hazardous waste disposal units to carry out harmless treatment, that is, by adding lime or slaked lime, it reacts into calcium fluoride and ammonia water; qualified disposal units will recycle ammonia water, and calcium fluoride will become sludge for harmless landfill. This disposal method is costly, polluting, and expensive for sludge disposal. The key is that resources are not effectively utilized, which is a method that does not make up for the gains.

[0004] Another treatment method is to add hydrofluoric acid to produce ammonium bifluoride products. Since ordinary industrial-grade ammonium bifluoride is produced using various fluorine-containing waste acids or by-product fluorine-containing acids, and the market capacity of ammonium bifluoride products is limited, it is necessary to expand the recycling routes and products of BOE waste liquid.

[0005] Hydrogen Fluoride, with a chemical formula of HF and a molecular weight of 20.01, is easily soluble in water and ethanol. Anhydrous hydrogen fluoride (AHF) is a colorless, transparent liquid at low temperatures or pressures, with a boiling point of 19.4°C, a melting point of -83.37°C, and a density of 1.008 g / cm 3 (water = 1). It is very easy to volatilize into white smoke at room temperature and normal temperature. Its chemical properties are very active and can react with alkali, metals, oxides and silicates. Hydrogen fluoride is the basis of modern fluorine chemical industry and the most basic raw material for producing elemental fluorine, various fluorine refrigerants, new fluorine-containing materials, inorganic fluoride salts, various organic fluorides, etc. Hydrogen fluoride and water can be mixed in any mass ratio to form hydrofluoric acid (abbreviated as HF).

[0006] Ammonium sulfate is an inorganic substance with the chemical formula (NH4)2SO4. It is colorless crystal or white granule and odorless. It decomposes above 280℃. Solubility in water: 70.6g at 0℃, 103.8g at 100℃. It is insoluble in ethanol and acetone. The pH of 0.1mol / L aqueous solution is 5.5, the relative density is 1.77, and the refractive index is 1.521. Ammonium sulfate is mainly used as a fertilizer and is suitable for various soils and crops. Ammonium sulfate has a huge market capacity.

[0007] Therefore, it is necessary to develop a BOE waste liquid treatment method and device to fully recycle the effective resources of BOE waste liquid. Summary of the invention

[0008] In view of the problems in the related art, the present invention proposes a BOE waste liquid treatment method and device to overcome the problem of the market capacity of ammonium bifluoride in the existing treatment method, and obtains hydrofluoric acid products and ammonium sulfate products with huge market capacity.

[0009] In order to solve the above technical problems, the present invention is achieved through the following technical solutions: A method for treating BOE waste liquid comprises the following steps: S1 Sulfuric acid replacement Under stirring conditions, adding concentrated sulfuric acid to the BOE waste liquid, and then continuing to stir to obtain a reaction liquid; S2 evaporation and fluorine extraction The reaction liquid is evaporated by normal pressure evaporation to obtain mixed steam, and the total content of ammonium sulfate and ammonium bisulfate in the evaporation residue is controlled to be 45%-55%; S3 fractionation and concentration The mixed steam is fractionated to control the HF content of the condensate at the top of the tower to be ≤1%, and the bottom of the tower is used to concentrate hydrofluoric acid to obtain a concentrated hydrofluoric acid product with an HF content of ≥20%; S4 Neutralization and Defluorination In the evaporation residual liquid, under stirring conditions, ammonia water, fluorinated gypsum emulsion, coagulant and flocculant are added in sequence; after the addition is completed, stirring is stopped and the liquid is naturally settled to obtain an upper clear liquid and a lower sludge; S5 Evaporation Crystallization The supernatant is concentrated, evaporated and crystallized to obtain a crystal slurry, and the crystal slurry is separated to obtain an ammonium sulfate product and a mother liquor.

[0010] In some embodiments, in step S1, the molar ratio of the added concentrated sulfuric acid to the ammonia nitrogen in the BOE waste liquid is 0.527:1 to 1:1. More preferably, the molar ratio of the added concentrated sulfuric acid to the ammonia nitrogen in the BOE waste liquid is 0.556:1.

[0011] In some embodiments, the mixed vapor is evaporated HF and water.

[0012] In some embodiments, the temperature of the atmospheric pressure evaporation is 105-106°C.

[0013] In some embodiments, the fractionation tower extraction and reflux volume ratio of step S3 is ≥ 1.055.

[0014] In some embodiments, the coagulant is polyaluminum sulfate; the flocculant is polyacrylamide PAM.

[0015] In some embodiments, the interval between adding the ammonia water and the fluorinated gypsum emulsion is 15-25 minutes; the interval between adding the fluorinated gypsum emulsion and the coagulant is 15-25 minutes. Specifically, after the addition of the ammonia water is completed, stirring is continued for 15-25 minutes; then the fluorinated gypsum emulsion is added, and after the addition of the fluorinated gypsum emulsion is completed, stirring is continued for 25-35 minutes; then the coagulant polyaluminium sulfate and the flocculant PAM are added dropwise.

[0016] In some embodiments, the mother liquor is sent back to the evaporation system for further evaporation and crystallization, wherein the evaporated gas is condensed to obtain ammonia nitrogen wastewater, which is sent to a sewage treatment plant for treatment.

[0017] A BOE waste liquid treatment device comprises: a displacement reactor, an evaporator, a neutralization reactor, a triple-effect evaporator and a centrifuge connected in sequence; The displacement reactor comprises a feeding port and a liquid discharge port, through which BOE waste liquid and concentrated sulfuric acid are successively added, and the reaction liquid obtained after sufficient stirring and reaction is discharged from the liquid discharge port; The evaporator is connected to the liquid discharge port and is used to evaporate the reaction liquid to obtain mixed steam and evaporated residual liquid; The neutralization reaction kettle is connected to the lower part of the evaporator; The triple-effect evaporator is connected to the neutralization reactor to evaporate and crystallize the supernatant at least once to obtain an ammonium sulfate crystal solution; The centrifuge is located at the rear of the triple-effect evaporator and centrifuges the ammonium sulfate crystal solution to obtain an ammonium sulfate product and a centrifuge mother liquor; Also includes: A fractionation tower connected to the upper part of the evaporator for fractionating the mixed steam to obtain concentrated hydrofluoric acid and waste water; The filter press is located at the rear of the neutralization reactor, and dehydrates the lower layer of sludge by filtering, and then sends it to the dryer, where it is dried to obtain a calcium fluoride product.

[0018] In some embodiments, the dehydrated waste liquid obtained by the filter press is transported to the triple-effect evaporator for evaporation and crystallization.

[0019] In some embodiments, the centrifugal mother liquor obtained from the centrifuge is refluxed to the triple-effect evaporator for re-evaporation and crystallization.

[0020] In some embodiments, an ammonium sulfate temporary storage tank is provided between the neutralization reactor and the triple-effect evaporator, and the dehydrated waste liquid obtained by the filter press is transported to the ammonium sulfate temporary storage tank.

[0021] The present invention has the following beneficial effects: The use of this solution to treat BOE waste liquid avoids the bottleneck of the market capacity of ammonium bifluoride, produces hydrofluoric acid products and ammonium sulfate products with huge market capacity, truly realizes the value orientation of turning waste into treasure, circular economy, and green environmental protection, and is suitable for industrial promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the invention, the drawings required for describing the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0023] Figure 1 This is a schematic structural diagram of a BOE waste liquid treatment device according to Example 1 of the present invention; in, 1-displacement reactor, 2-evaporator, 3-neutralization reactor, 4-triple effect evaporator, 5-centrifuge, 6-fractionation tower, 7-filter press, 8-dryer, 21-reaction liquid temporary storage tank, 22-ammonium sulfate temporary storage tank. DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] Example 1 Reference Figure 1 As shown, a BOE waste liquid treatment device includes: a displacement reactor 1, an evaporator 2, a neutralization reactor 3, a triple-effect evaporator 4, a centrifuge 5, a distillation tower 6, a filter press 7, and a dryer 8 connected in sequence.

[0026] The displacement reactor 1 includes a dosing port and a drain port, through which BOE waste liquid and concentrated sulfuric acid are added in sequence, and the reaction liquid obtained after sufficient stirring and reaction is discharged from the drain port. The evaporator 2 is connected to the drain port to evaporate the reaction liquid to obtain mixed steam and evaporation residue. The neutralization reactor 3 is connected to the lower part of the evaporator 2 to receive the evaporation residue, and after sequentially adding ammonia water and fluorgypsum emulsion, the upper clear liquid and the lower sludge are obtained by sedimentation separation. The triple-effect evaporator 4 is connected to the neutralization reactor 3 to evaporate and crystallize the upper clear liquid at least once to obtain an ammonium sulfate crystal solution. The centrifuge 5 is located at the rear of the triple-effect evaporator 4, and centrifuges the ammonium sulfate crystal solution to obtain an ammonium sulfate product and a centrifuge mother liquor.

[0027] The fractionation tower 6 in the present invention is connected to the upper part of the evaporator 2 to fractionate the mixed steam to obtain concentrated hydrofluoric acid and waste water. The filter press 7 is located at the rear of the neutralization reactor 3, and the lower layer of sludge is filtered and dehydrated, and sent to the dryer 8, which is dried by the dryer 8 to obtain calcium fluoride products (fluorite balls).

[0028] In order to store the reaction liquid obtained from the displacement reactor, a reaction liquid temporary storage tank 21 is provided at the front of the evaporator 2. The reaction liquid temporary storage tank 21 can better realize the continuous production of the subsequent process.

[0029] It is worth noting that the wastewater obtained from the fractionation tower 6 in the present invention is discharged after being treated, and the wastewater contains only a trace amount of HF.

[0030] The dehydrated waste liquid obtained by the filter press 7 in the present invention is transported to the triple-effect evaporator 4 for evaporation and crystallization, so that the waste liquid can be recovered more effectively, especially the ammonium sulfate product in the waste liquid. Similarly, the centrifuged mother liquor obtained by the centrifuge 5 in the present invention is refluxed to the triple-effect evaporator 4 for re-evaporation and crystallization.

[0031] In order to achieve better continuous production, an ammonium sulfate temporary storage tank 22 is provided between the neutralization reactor 3 and the triple-effect evaporator 4 , and the dehydrated waste liquid obtained by the filter press 7 is transported to the ammonium sulfate temporary storage tank 22 .

[0032] The BOE waste liquid used in the following examples is the waste liquid after chip cleaning, and its composition is shown in Table 1. The other chemical reagents used are all commercially available products, and the equipment used is the equipment in Example 1.

[0033] Table 1 BOE waste liquid composition .

[0034] Embodiment 2-4 A method for treating BOE waste liquid comprises the following steps: The first step is sulfuric acid replacement 500 kg of BOE waste liquid was pumped into the displacement reactor, and a certain amount of 98% concentrated sulfuric acid was added to the BOE waste liquid under stirring conditions. After the addition was completed, stirring was continued for 20 minutes, and the obtained reaction liquid was discharged from the discharge port and moved to the reaction liquid temporary storage tank. Relevant data are shown in Table 2.

[0035] Table 2 Raw material dosage table (unit: Kg) .

[0036] The second step is evaporation and fluorine extraction The reaction liquid is pumped into the evaporator and evaporated by atmospheric pressure evaporation. The atmospheric pressure evaporation temperature is 105-106°C. Most of the HF and water are evaporated, and the total content of ammonium sulfate and ammonium bisulfate in the evaporation residue is controlled to be 45%-55%. The evaporated mixed steam and evaporation residue are transferred to subsequent processes respectively. Relevant data are shown in Table 3.

[0037] Table 3 Quantity and composition of evaporation residue .

[0038] The third step is fractionation and concentration The mixed steam (evaporated HF and water) in step 2 is introduced into the fractionation tower for fractionation, and the reflux ratio is controlled to be ≥1.055 to obtain acidic wastewater with an HF content of ≤1% in the tower top condensate. The tower bottom is a concentrated hydrofluoric acid product with an HF content of ≥20%. When the HF content is ≥20%, it meets the use requirements of glass thinning and other industries, and the acidic wastewater produced from the tower top is sent to the sewage station for treatment. Relevant data are shown in Table 4.

[0039] Table 4 Concentrated acid quantity and composition .

[0040] Step 4: Neutralization and defluorination Pump the evaporation residual liquid into the neutralization reactor, add a certain amount of 20% ammonia water under stirring conditions, and continue stirring for 20 minutes after the addition of ammonia water is completed; slowly add a certain amount of 20% fluorine gypsum emulsion, and continue stirring for 30 minutes after the addition of the emulsion is completed; then drop coagulant polyaluminum sulfate and flocculant PAM, stop the agitator, and settle naturally to obtain the upper clear liquid and the lower sludge. The sludge is filtered to obtain sludge with a high calcium fluoride content, which can be used as an additive for steel smelting after balling. Specific data are shown in Table 2.

[0041] Step 5: Evaporation and crystallization The supernatant liquid is pumped into a three-effect evaporator for concentration, evaporation and crystallization to obtain a crystal slurry. The crystal slurry is separated by a centrifuge to obtain an ammonium sulfate product and a centrifugal mother liquor. The centrifugal mother liquor is sent back to the three-effect evaporator for further concentration, evaporation and crystallization. The evaporated gas is condensed to obtain ammonia nitrogen wastewater, which is sent to a sewage station for treatment. Specific data are shown in Tables 5 and 6.

[0042] Table 5 Quantity and composition of ammonium sulfate products .

[0043] Table 6 Quantity and composition of ammonia nitrogen wastewater .

[0044] Step 6: Drying Fluorite The lower layer of sludge in the fourth step is pumped into the filter press for filtration to obtain calcium fluoride sludge and mother liquor, and the mother liquor is recycled to the triple-effect evaporator in the fifth step for concentration, evaporation and crystallization; the calcium fluoride sludge is dried in a dryer to obtain the calcium fluoride product (fluorite ball). Specific data are shown in Table 7.

[0045] Table 7 Quantity and composition of spherical calcium fluoride .

[0046] This scheme is used to treat BOE waste liquid, and the hydrogen fluoride in the BOE waste liquid is replaced with sulfuric acid, and hydrofluoric acid is recovered by evaporation and fractionation. The evaporated residual liquid is neutralized with ammonia to obtain a fluorine-containing ammonium sulfate solution, and then defluorinated with fluorinated gypsum slurry to obtain a low-fluorine ammonium sulfate solution, which is concentrated and crystallized to obtain an ammonium sulfate product. Both hydrofluoric acid solution and ammonium sulfate have huge market capacity. The bottleneck of the market capacity of ammonium bifluoride is avoided, and hydrofluoric acid products and ammonium sulfate products with huge market capacity are produced.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for treating BOE waste liquid, characterized in that: The steps include: S1 Sulfuric acid replacement Under stirring conditions, adding concentrated sulfuric acid to the BOE waste liquid, and then continuing to stir to obtain a reaction liquid; S2 evaporation and fluorine extraction The reaction liquid is evaporated by normal pressure evaporation to obtain mixed steam, and the total content of ammonium sulfate and ammonium bisulfate in the evaporation residue is controlled to be 45%-55%; S3 fractionation and concentration The mixed steam is fractionated to control the HF content of the condensate at the top of the tower to be ≤1%, and the bottom of the tower is used to concentrate hydrofluoric acid to obtain a concentrated hydrofluoric acid product with an HF content of ≥20%; S4 Neutralization and Defluorination In the evaporation residual liquid, under stirring conditions, ammonia water, fluorinated gypsum emulsion, coagulant and flocculant are added in sequence; after the addition is completed, stirring is stopped and the liquid is naturally settled to obtain an upper clear liquid and a lower sludge; S5 Evaporation Crystallization The supernatant is concentrated, evaporated and crystallized to obtain a crystal slurry, and the crystal slurry is separated to obtain an ammonium sulfate product and a mother liquor.

2. The method for treating BOE waste liquid according to claim 1, characterized in that: In step S1, the molar ratio of the added concentrated sulfuric acid to the molar ratio of ammonia nitrogen in the BOE waste liquid is 0.527:1 to 1:

1.

3. The method for treating BOE waste liquid according to claim 1, characterized in that: The mixed steam is the evaporated HF and water.

4. The method for treating BOE waste liquid according to claim 1, characterized in that: The coagulant is polyaluminium sulfate; the flocculant is polyacrylamide PAM.

5. The method for treating BOE waste liquid according to claim 1, characterized in that: The interval time for adding the ammonia water and the fluorinated gypsum emulsion is 15-25 minutes; the interval time for adding the fluorinated gypsum emulsion and the coagulant is 15-25 minutes.

6. The method for treating BOE waste liquid according to claim 1, characterized in that: The mother liquor is sent back to the evaporation system for further evaporation and crystallization, wherein the evaporated gas is condensed to obtain ammonia nitrogen wastewater, which is sent to a sewage station for treatment.

7. A BOE waste liquid treatment device, characterized in that: include: A displacement reactor, an evaporator, a neutralization reactor, a triple-effect evaporator and a centrifuge connected in sequence; The displacement reactor comprises a feeding port and a liquid discharge port, through which BOE waste liquid and concentrated sulfuric acid are successively added, and the reaction liquid obtained after sufficient stirring and reaction is discharged from the liquid discharge port; The evaporator is connected to the liquid discharge port and is used to evaporate the reaction liquid to obtain mixed steam and evaporated residual liquid; The neutralization reaction kettle is connected to the lower part of the evaporator; The triple-effect evaporator is connected to the neutralization reactor to evaporate and crystallize the supernatant at least once to obtain an ammonium sulfate crystal solution; The centrifuge is located at the rear of the triple-effect evaporator and centrifuges the ammonium sulfate crystal solution to obtain an ammonium sulfate product and a centrifuge mother liquor; Also includes: A fractionation tower connected to the upper part of the evaporator for fractionating the mixed steam to obtain concentrated hydrofluoric acid and waste water; The filter press is located at the rear of the neutralization reactor, and dehydrates the lower layer of sludge by filtering, and then sends it to the dryer, where it is dried to obtain a calcium fluoride product.

8. A BOE waste liquid treatment device according to claim 7, characterized in that: The dehydrated waste liquid obtained by the filter press is transported to the triple-effect evaporator for evaporation and crystallization.

9. A BOE waste liquid treatment device according to claim 7, characterized in that: The centrifugal mother liquor obtained by the centrifuge is refluxed to the triple-effect evaporator for re-evaporation and crystallization.

10. A BOE waste liquid treatment device according to claim 7, characterized in that: An ammonium sulfate temporary storage tank is provided between the neutralization reactor and the triple-effect evaporator, and the dehydrated waste liquid obtained by the filter press is transported to the ammonium sulfate temporary storage tank.

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